1. Field of the Invention
The invention relates to an improved method for the preparation of 1,3-disubstituted 4,5-cis-dicarboxy-2-imidazolidones by reacting the corresponding substituted 2,3-diaminosuccinic acid with phosgene.
Description of the Prior Art
The products of this process, particularly the 1,3-diallyl- and 1,3-dibenzyl-substituted 4,5-cis-dicarboxy2-imidazolidones are important intermediate products for the preparation of Vitamin H, also referred to as biotin (see J.A.C.S. 100, 1978, page 1558, and U.S. Pat. No. 2,489,232). Said references describe a method for the preparation of said intermediates where the corresponding diaminosuccinic acid is reacted in a strongly alkaline solution (pH 13-14) to obtain the desired imidazolidones by adding dropwise a solution of phosgene in an inert organic solvent such as xylene or toluene, while simultaneously adding an alkali metal hydroxide. Since the reaction takes place in a twophase system of xylene/water and/or toluene/water in a strongly alkaline medium at pH &gt;12, the 2,3-bis(allylamino)succinic acid reactant is present in the dissolved form.
This prior art method has serious drawbacks for technical implementation. Due to the high pH value of the reaction mixture, a large part of the phosgene is destroyed by hydrolysis. Therefore, a large excess of phosgene must be used. This in turn results in a large amount of undesirable salt production. Furthermore, problems with the reaction vessel materials result since the reaction medium is strongly corrosive as a result of the continuously increasing chloride ion concentration and since the work is also carried out at high pH (pH &gt;12).
Furthermore, this prior art method requires the use of a phosgene solvent which is not miscible with water which reduces the reaction time and yield and further complicates processing. It has been found that conversion and yield fluctuate greatly when employing the known method. It was therefore the purpose of this invention to improve the prior art process in such a manner that the reaction can be carried out in a simpler and more economical manner with fewer problems concerning the materials of the reaction vessels.